Weld-plating of steel

ABSTRACT

A steel base containing enough carbon to be heat-treatable or hardened is surface decarbonized prior to being weld-plated with another metal, such as austenitic stainless steel, to avoid cracking of the base from the welding heat.

1 WELD-PLATING OF STEEL [75] Inventor:

[73] Assignee: Siemens Akliengesellschaft, Munich,

Germany [22] Filed: Aug. 17, 1972 [21] Appl. No; 281,555

Werner Debray, Erlangen. Germany [30] Foreign Application Priority Data Aug 25, 1971 Germany 2142461] [52] US. Cl. 219/76; 117/50; 148/16 [51] Int. Cl 323k 1/20 I58] Field of Search 148/13. 16.5.14 15.5. 148/161), 19. 34, 127, 16, 6.14; 117/50 49 51; 219/76 156] References Cited UNITED STATES PATENTS 1185.814 5/1965 Russncr c1211. 219/76 June 24, 1975 3,406,047 10/1968 Magor ct a1. 148/16 3.4993103 3/1970 Hcnrickson cl a1 l 1 1 l 148/34 3.607.458 9/1971 Hunsaker or al l 1 148/16 3.694271 9/1972 Egncll n 148/34 Primary Examiner-Charles E. Van Horn Axxismn! Examiner-Jerome W. Massie Attorney, Agent, or Firm-Kenyon & Kenyon Reilly Carr 84 Chapin [57 1 ABSTRACT A steel base containing enough carbon to he heatlreatable or hardened is surface decarbonized prior to being weld-plated with another metal, such as austenilic stainless steel, to avoid cracking of the base from the welding heat.

4 Claims, No Drawings WELD-PLATING OF STEEL BACKGROUND OF THE INVENTION The present invention relates to the process of weldplating workpieces of one metal with another metal. In particular it is concerned with weld-plating non-rusting or stainless austenitic steels or high-alloy wear resistant metals on workpieces made of hardenable or heat treatable steels which therefore contain appreciable amounts of carbon. Such weld-platings are often needed to make certain surfaces, for example, the inner walls of boilers, resistant to corrosion or to wear. The chief fields of application are nuclear-reactor technology, processing technology in the chemical industry, and also the machine building industry.

DESCRIPTION OF THE PRIOR ART The weld-plating process itself is extensively used. However, particularly in the case of the hardenable or heat-treatable steels, it is possible for cracking of the part being plated to occur in the region subjected to the influence of the heat, or cracking may occur after the plating operation. Under certain conditions this can impair the utility of the part. Furthermore. problems are encountered when the basic material and the plating material cannot be welded to one another by normal practices; for example, a buffering welding prior to the actual welding-plating may be necessary.

SUMMARY OF THE INVENTION One object of the present invention is to avoid the cracking described above and, in general, to weldplated parts made of steel containing enough carbon to be hardenable, with metals of another type, such as austenitic stainless steel. in an improved manner.

According to this invention. this object is attained by first surface decarbonizing the steel part, and then weld-plating the part. The effect is that a relatively low carbon steel surface is weld-plated. Particularly, the weld-plating with austenitic stainless steel is facilitated. The cracking of the steel surface subjected to the weldplating heat is avoided.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In accordance with the invention, a pre-treatment is used which consists of decarbonizing the steel surface to be plated, to a depth of approximately 1 to 5 mm. For example, this decarbonizing operation can be effected by a heat treatment of up to l,O00C. maximum, and preferably from 800 to 900C, in a decarbonizing gas atmosphere. Another possibility consists of coating the surface which is to be decarbonized with a l to 2 mm thick layer of a paste having a decarbonizing action, followed by a heat treatment in a protective-gas atmosphere at the aforesaid temperatures. with removal of the applied layer prior to the actual weld- 2 plating operation.

Gases effective in this process are the so-called forming gases, e.g., mixtures of nitrogen and 20% hydrogen, or a mixture of hydrogen, carbon dioxide and carbon monoxide, or a hydrogen-argon mixture or other combinations having the same effect. The time needed for the decarbonizing depends on the carbon content of the steel, on the temperature used and on the hydrogen content or the decarbonizing power of the gas. The higher the temperature, the shorter the necessary heat treatment time. Parts of the surface of the material that are not to be plated or decarbonized may be covered with suitable protective pastes, as is known from case-hardening technology.

The degree of decarbonization should be carried as far as possible. For example, a carbon-steel with 0.6% of carbon should have a surface layer containing less than 0.15% carbon. In order to obtain a decarbonization from 0.2% down to 0.6%, for a depth of about 3 mm. a heating time of 5 hours is needed at a temperature of 900C. The depth of decarbonization depends on the so-called penetration by burning during the plating process. The less this is, the less can be the decarbonizing depth, and the shorter the pre-treatment time.

Extensive experimentation and testing of this new process have shown that subsequent cracking can definitely be avoided, and that the material to be plated does not need to be pre-tested as to the possibility of weld-plating it. This process thus offers not only purely technological advantages, but offers also substantially greater freedom of choice as to the basic material of the workpieces to be plated.

Some parts to be weld-plated may be too large for the available decarbonizing furnace. Often these parts are fabricated from separate parts which are not individually too large. The separate parts may be processed as described hereinabove including the weld-plating, and the parts then welded together, the weld connections often being amenable to usual plating methods.

I claim:

1. A process for weld-plating austenitic stainless steel on the surface of a hardenable carbon steel part; wherein the improvement comprises decarbonizing said surface and thereafter weld-plating the stainless steel thereon.

2. The process ofclaim l in which said decarbonizing is extended into said surface for a depth at least equal to the penetration of the surface by burning during said weld-plating.

3. The process of claim 2 in which said depth is approximately from I to 5 mm.

4. The process of claim 3 in which by said decarbonizing the carbon content of said carbon steel is reduced to less than 0.15% substantially throughout said depth. 

1. A PROCESS FOR WELD-PLATING AUSTENITIC STAINLESS STEEL ON THE SURFACE OF A HARDENABLE CARBON STEEL PART; WHEREIN THE IMPROVEMENT COMPRISES DECARBONIZING SAID SURFACE AND THEREAFTER WELD-PLATING THE STAINLESS STEEL THEREON.
 2. The process of claim 1 in which said decarbonizing is extended into said surface for a depth at least equal to the penetration of the surface by burning during said weld-plating.
 3. The process of claim 2 in which said depth is approximately from 1 to 5 mm.
 4. The process of claim 3 in which by said decarbonizing the carbon content of said carbon steel is reduced to less than 0.15% substantially throughout said depth. 